This invention pertains to an electric power source apparatus including an electric power converter circuit for converting an output of an AC power source into a DC output or a DC power source into an AC output having an arbitrary frequency.
There has been used an electric power source apparatus including an electric power converter circuit such as an inverter or cycloconverter for converting an output of an electric power source into a predetermined DC output or AC output. For instance, an inverter generator apparatus which is adapted to supply an output of a generator to an inverter and to obtain from the inverter a DC output having a predetermined magnitude or an AC output having a predetermined frequency and magnitude has been used as the generator apparatus having an electric source of a generator driven by a prime mover such as an internal combustion engine.
The inverter circuit used in such an inverter generator apparatus comprises a rectifier to rectify an output of an AC generator, a switch circuit in the form of a bridge circuit of on-off controllable switch elements and a filter circuit to remove an excessive frequency component from an output of the switch circuit. The output of the inverter is applied across the load connection terminals. Such a generator apparatus also comprises a load voltage detection circuit to detect a load voltage across the load connection terminals, a load current detection circuit to detect a load current flowing through the load connection terminals and a controller to control the switch elements in accordance with the voltage detected by the load voltage detection circuit and the load current detected by the load current detection circuit. The rectified output of the generator is adapted to be converted into the DC output having an arbitrary magnitude (an average value) or the DC output of the generator is adapted to be converted into the AC output having arbitrary frequency and magnitude.
In the generator apparatus, the AC output of the generator is converted by the rectifier into a constant DC voltage which is input to the switch circuit. The controller controls the output of the switch circuit by a pulse width modulation (PWM) system by turning on or off the switch elements on upper and lower sides of the bridge circuit while applying a drive signal to the diagonally disposed switch elements of the switch bridge circuit as the switch circuit so as to simultaneously turn on them during a half cycle of a predetermined sine. The voltage output from the switch circuit is applied through the load connection terminals to the load after it is converted into a smooth sinewave voltage through the filter circuit.
The sinewave voltage applied to the load terminals is detected by the load voltage detection circuit and fedback to the controller. The controller compares the instant magnitude of the output voltage with the instant value (the set value) of the predetermined sinewave voltage. The controller generates the predetermined sinewave voltage applied across the load connection terminals so that as the controller judges that the instant value of the output voltage is lower than the instant value of the predetermined sinewave voltage, it increases the duty ratio of the pulse width modulation control and as it judges that the instant value of the output voltage is higher than the instant value of the predetermined sinewave voltage, it decreases the duty ratio of the pulse width modulation control.
Also, the controller controls the overcurrent so that as the load current detected by the load current detection circuit exceeds the set value of the load current or detects the overcurrent, it stops outputting the drive signal applied to the switch elements of the switch circuit. This overcurrent control stops the output of the inverter circuit when the overcurrent flows so as to protect the switch elements of the inverter circuit.
Such an electric power apparatus can provide the voltage of predetermined frequency to the load terminals in spite of the revolution number of the generator because the DC voltage output from the rectifier can be converted into the AC voltage of arbitrary frequency by controlling the inverter circuit. Also, the apparatus can provide the DC voltage of arbitrary magnitude or average value by applying the drive signal to the diagonally disposed switch elements of the switch circuit to control one of the diagonally disposed switch elements to be turned on or off with the predetermined duty ratio.
In case that the volume of the load is relatively large, there are sometimes required to operate the two electric power source units in parallel. In this parallel operation of the two electric power source units, the corresponding two load connection terminals of the two electric power source units are connected to each other so as to simultaneously supply the electric power from the two electric power source units. The voltages generated by the two electric power source units, respectively are required to have the same frequency, the same magnitude and the same phases. If the frequencies or phases of the voltages generated by the two electric power source units are inconsistent due to some causes, the load current introduced from one of the electric power source units flows as the overcurrent into the other electric power source unit. This overcurrent control causes the output of the electric power source circuit to stop, which prevents the load from being normally driven.
It will be conceived that in order to operate the two electric power source units in parallel, the electric power converter circuits of the two electric power source units are controlled by a common controller to prevent the frequencies and the phases from being inconsistent. This will disadvantageously causes the construction of the electric power source units to be more complicated.
Accordingly, it is a principal object of the invention to provide an electric power source apparatus having an electric power converter circuit adapted to more easily operate two electric power source units in parallel without any complicated construction.
It is another object of the invention to provide a method of controlling an electric power source apparatus having an electric power converter circuit adapted to more easily operate two electric power source units in parallel without any complicated construction.
A first aspect of the present invention can be applied to an method of controlling an electric power source apparatus comprising an electric power converter circuit having on-off controllable switch elements to convert an output of an electric power source into predetermined DC or AC output by switching the switch elements and a pair of load connection terminals across which is applied an output of the electric power converter circuit while the electric power source apparatus is allowed to be driven in the condition that a voltage from another electric power source is allowed to be applied across the load connection terminals.
The method of the present invention can be accomplished by detecting a waveform of a voltage across the load connection terminals after the output of the electric power converter circuit is stopped when an overcurrent flows through the load connection terminals from the electric power converter circuit and judging whether the overcurrent is caused by an increase in the loads or by the voltage applied across the load connection terminals.
The output of the electric power converter circuit is kept stopped when it is judged that the overcurrent is caused by the increase in the load exceeding an allowable value. The output of the electric power converter circuit is restored in the condition in which the switch elements are so controlled that the waveform of the voltage applied across the load connection terminals from the electric power converter circuit is consistent with a waveform of the voltage across the load connection terminals detected by the voltage waveform detection step when it is judged that the overcurrent is caused by the voltage applied across the load connection terminals form another power source, but not by the increase in the load exceeding the allowable value.
With the aforementioned control made, since the waveform of the voltage applied across the load connection terminals from the electric power converter circuit is consistent with the waveform of the voltage applied across the load connection terminals form another power source, the electric power converter circuit and another power source can be operated in parallel without any trouble.
In the invention, xe2x80x9canother power sourcexe2x80x9d applied across the load connection terminals may be an AC or DC electric power source formed in an arbitrary manner. It may be another electric power source apparatus formed in the same manner as that to which the present invention is applied or formed in a different manner. It may be also an AC electric power source having no electric power converter circuit. Further, xe2x80x9canother electric power sourcexe2x80x9d may be a DC electric power source such as a battery or commercial electric power source.
A second aspect of the present invention can be applied to an electric power source apparatus comprising an electric power converter circuit having on-off controllable switch elements to convert an output of an electric power source into predetermined DC or AC output by switching the switch elements, a pair of load connection terminals across which is applied the output of the electric power converter circuit, a load voltage detection circuit to detect a voltage across the load connection terminals, a load current detection circuit to detect a load current flowing through the load connection terminals and a controller to control the switch elements of the electric power converter circuit in accordance with the voltage detected by the load voltage detection circuit and the load current detected by the load current detection circuit with the electric power source apparatus allowed to be driven in the condition that a voltage from another electric power source is also applied across the load connection terminals.
In this invention, the controller may include output waveform storage means to store waveform data for specifying an waveform of the voltage detected by the load voltage detection circuit while the output of the electric power converter circuit is stopped when an overcurrent is detected by the load current detection circuit, overcurrent cause judgement means to judge from the condition of the voltage stored by the output waveform storage means whether the overcurrent is caused by the increase in the load exceeding an allowable value or by the voltage applied across the load connection terminals form another power source and switch control means to control the switch elements so that the output of the electric power converter circuit is kept stopped when it is judged that the overcurrent is caused by the increase in the load exceeding the allowable value while the output of the electric power converter circuit is restored in the condition wherein the waveform of the voltage applied across the load connection terminals from the electric power converter circuit is consistent with a waveform specified by the waveform data stored by the output waveform storage means when it is judged that the overcurrent is caused by the voltage applied across the load connection terminals form another power source, but not by the increase in the load exceeding the allowable value.
Although, with the aforementioned construction made, the waveform of the voltage applied across the load connection terminals from the electric power converter circuit is controlled so as to be consistent with the waveform specified by the waveform data stored by the voltage applied across the load connection terminals from another electric power source, the switch elements may be so controlled that the waveform data of the voltage across the load connection terminals is detected in the condition that the output of the electric power converter circuit is stopped during a period required for detecting the waveform data to specify the waveform of the voltage across the load connection terminals.
In this case, the controller may include output waveform storage means to store the waveform data for specifying an waveform of the voltage detected by the load voltage detection circuit while the output of the electric power converter circuit is stopped for a set detection period and switch control means to control the switch elements of the electric power converter circuit so that the waveform of the voltage applied across the load connection terminals from the electric power converter circuit is consistent with the waveform specified by the waveform data stored by the output waveform storage means.
With the aforementioned control made, although the electric power converter circuit is stopped during the period required for specifying the waveform of the voltage across the load connection terminal, such a period may be properly xc2xd cycle through 2 or 3 cycles with the commercial electric power source used. Thus, since the period can be reduced to less than 60 msec., there is no actual trouble.
In this invention, an inverter circuit may be used for the electric power converter circuit, the electric power source apparatus may further comprise charge command generation means to generate a charge command to command a battery to be charged when the battery is connected as the load across the load connection terminals and the controller may further includes polarity judgement means to judge the polarity of the battery when the battery is connected across the load connection terminals whereby the switch elements of the inverter circuit is so controlled as to apply the DC voltage having a magnitude and a polarity suitably enough to charge the battery across the load connection terminals from the inverter circuit in accordance with the battery terminal voltage detected by the load voltage detection circuit and the battery polarity judged by the polarity judgement means when the charge command generation means generates the charge command.
In this manner, the battery can be charged by applying the charge command from the charge command generation means to the controller when the battery is connected across the load connection terminals. Also, in this case, since the battery can be connected across the load connection terminals without any awareness of the battery polarity, the treatment can be more easily made.